1. Field of the Invention
This invention relates to a heat pump protection system. More specifically the invention relates to a diagnostic monitor system for heat pump protection.
2. Description of the Prior Art
The use of a heat pump system, wherein a single unit is employed for both heating and cooling, has in recent years become well established and economically acceptable in many residential and commercial applications. Such a system typically involves a pair of condensor/evaporator coils, one physically located inside the building and the other outside the building, connected to a single motor/compressor wherein the heating versus cooling roles are interchangeable by appropriate valving.
It is generally recognized that there are specific operating limits within which the motor/compressor system must remain in order to prevent damage to the system. Thus it is an accepted practice in the industry to provide the motor/compressor with an electrical protection system. It is known that this system will involve an electric current lock-out relay which is used in series with the low voltage coil of the compressor motor contactor. This contactor interrupts the power supply to the compressor motor when either of two conditions occurs. Usually a 24 volt AC safety circuit is provided to monitor these conditions and includes a high pressure switch on the condensor side of the compressor and a low temperature switch on the evaporator side of the compressor. These respective low voltage switches will open upon experiencing either a high pressure condition, possibly indicating a blockage in the heat pump system, or a low temperature condition, possibly indicating leakage of the refrigerant, and will remain open for a time span, measured in terms of milliseconds, during which the lock-out relay is activated terminating the power to the compressor motor. The high pressure switch or the low temperature switch will then reset itself and thus be ready to again signal a critical condition upon restarting the compressor motor. Various other more elaborate protection systems have been suggested and employed involving time delay restart circuits, current sensing, voltage drop sensing, monitoring other thermal parameters, and the like. However, these systems are directed primarily to protecting the heat pump rather than to diagnostically evaluating what caused the system turndown. Thus, in such cases, the repairman must attach a monitoring device and reinitiate the undesirable event before identifying and repairing a faulty component or condition. This prior art practice has not been completely satisfactory in that it frequently involves repeated trips to the malfunctioning unit and the additional risk of damage in that the system must be restarted before any specific cause of the turndown can be identified with certainty.